Novavax NVX-COV2373 triggers neutralization of Omicron sub-lineages

The SARS-CoV-2 Omicron (B.1.1.529) Variant of Concern (VOC) and its sub-lineages (including BA.2, BA.4, BA.5, BA.2.12.1) contain spike mutations that confer high level resistance to neutralizing antibodies induced by vaccination with ancestral spike or infection with previously circulating variants. The NVX-CoV2373 vaccine, a protein nanoparticle vaccine containing the ancestral spike sequence, has value in countries with constrained cold-chain requirements. Here we report neutralizing titers following two or three doses of NVX-CoV2373. We show that after two doses, Omicron sub-lineages BA.1 and BA.4/BA.5 were resistant to neutralization by 72% (21/29) and 59% (17/29) of samples respectively. However, after a third dose of NVX-CoV2373, we observed high titers against Omicron BA.1 (GMT: 1,197) and BA.4/BA.5 (GMT: 582), with responses similar in magnitude to those triggered by three doses of an mRNA vaccine. These data are of particular relevance as BA.4/BA.5 is dominating in multiple locations, and highlight the potential utility of the NVX-CoV2373 vaccine as a booster in resource-limited environments.

We next compared neutralization of Omicron BA.1 and BA.4/BA.5 following multi-dose regimens of adenoviral, mRNA and protein-based vaccines. We tested samples after 2 doses of the adenoviral or 3 doses of the mRNA vaccines, given that these are currently offered as booster regimens in South Africa. These sera were collected from 11 individuals who received the AD26.COV2S vaccine (73% were female and all were over 30 years of age) and nine individuals who received the BNT162b2 vaccine (100% female and 22% were under 29 years of age, Supplementary table 1). As expected, 2 doses of AD26.COV2.S elicited ten-and 14-fold lower GMT against BA.1 than 3 doses of the BNT162b2 and NVX-CoV2373 vaccines respectively (Fig. 2). Similarly the 2 dose AD26.COV2.S vaccine elicited 12-and 11-fold lower GMT against BA.4/BA.5 than 3 does of either the BNT162b2 and NVX-CoV2373 vaccines. All third dose BNT162b2 and NVX-CoV2373 plasma were able to neutralize Omicron BA.1 and BA.4/BA.5, while only 13-50% of the two dose AD26.COV2.S samples had neutralizing activity against these Omicron sub-lineages. The NVX-CoV2373 third dose plasma GMT against BA.1 and BA.4/BA.5 was comparable to the BNT162b2 titres.

Discussion
In summary, we report enhanced neutralization of Omicron BA.1 and BA.4/BA.5 following three doses of the NVX-CoV2373 vaccine with responses comparing well to three doses of an mRNA vaccine. We note that 6 months after two doses of NVX-CoV2373, increased binding antibodies were reported, suggesting that responses after the third dose may mature further 10 . As durability of vaccine platforms varies, future studies should assess this for NVX-CoV2373 neutralization at later time-points 10 . The two dose NVX-CoV2372 vaccine regimen elicits robust memory CD4 + and CD8 + T cell responses in 100% and 65% of individuals respectively 7,10 . www.nature.com/scientificreports/ In addition, the two dose regimen induces antibodies with multiple Fc-mediated functions, which in non-human primate and human cohorts likely contribute to protection from infection 10 . This T cell and Fc effector function data, which is unlikely to differ following a third dose of the NVX-CoV2373 vaccine, coupled with neutralizing antibodies we have described here, suggests that this vaccine is likely to prevent severe disease after SARS-CoV-2 breakthrough infection with Omicron BA.4/5 sub-lineages (Supplementary Table 1).
Limitations of the study include the difference in timing of the sample collection following the second and third dose of the NVX-CoV2373 vaccine, with collection at 14 days and 1 month post vaccination respectively. Similarly, sample collection following administration of the AD26COV2.S and BNT162b2 booster doses varies between 1 and 3 months and includes relatively small sample numbers. Despite these limitations, this study highlights the neutralizing titres elicited by a third dose of the NVX-CoV2373 against currently circulating Omicron sub-lineages, which supports the use of this vaccine as a booster regimen 17 in countries where mRNA cold chain requirements cannot be met due to limited infrastructure.

Samples and ethics approvals. Individuals vaccinated with two or three doses of the NVX-CoV2373
vaccine were sampled at 14 days after the second dose or 35 days after the third dose. The third NVX-CoV2373 dose was administered 6 months after the first dose. This trial is registered under the ClinicalTrials.gov number, NCT04533399 (registered 17/09/2020), and the protocol was approved by the South African Health Products Regulatory Authority and by the institutional review board at each trial centre as described in detail by Shinde and colleagues 13 . Health care workers vaccinated with two dose of AD26.COV2.S (5 × 10 10 viral particles) as part of the Sisonke implementation trial were sampled at 2 months after vaccination. This trial is registered under the ClinicalTrials.gov number, NCT05148845, and the protocol was approved by the South African Health Products Regulatory Authority. These Sisonke individuals were recruited at the National Institute for Communicable Diseases (NICD), Johannesburg. Individuals vaccinated with two and three doses of the BNT162b22 vaccine were sampled at 2 months after the second dose or 1-3 months after the third dose and were recruited from Johannesburg. This study was given ethics approval by the University of the Witwatersrand Human Research Ethics Committee (Medical) M210465. All individuals provided written informed consent and all research was performed in accordance with the relevant guidelines/regulations and in accordance with the Declaration of Helsinki.

Data availability
All data reported in this paper will be shared by the lead contacts, Penny L. Moore (pennym@nicd.ac.za) and Shabir Madhi (Shabir.Madhi@wits.ac.za) upon request. This paper does not report original code.